The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Tag: Improvements

Making the world a better place, one piece at a time

Shower Curtain Magnet Anchors

Back in the day, bathtubs had a porcelain coating over a cast-iron carcass, so embedding little magnets in shower curtains worked perfectly to keep the loose ends from billowing out of the tub. Surprisingly, even here in the future, with plastic bathtubs ruling the land, some shower curtains still have magnets. The mud-job tile walls of shower stall in the Black Bathroom have nary a trace of iron, but we though I could add ferrous targets for a new shower curtain, thusly:

Shower Curtain Anchor – installed

The magnet lives inside a heat-sealed disk, so it’s (more-or-less) isolated from the water. As you’d expect, it’s a cheap ceramic magnet, not a high-performance neodymium super magnet, with no more strength than absolutely necessary to work under the most ideal of conditions.

My anchors must also be waterproof, firmly attached, non-marking, easily removable, and no more ugly than absolutely necessary. The general idea is to slice the bottom from a pill bottle, entomb a thin steel disk in epoxy, and attach to the tile with a patch of outdoor-rated foam tape.

So, we begin …

Cutting a narrow ring from a pill bottle requires a collet around the whole circumference, which started life as some sort of stout aluminum pole:

Shower Curtain Anchor – cutting tube stock

Bore out the inside, with a small step to locate the bottle:

Shower Curtain Anchor – boring fixture

Clean up the outside, just for pretty:

Shower Curtain Anchor – turning fixture OD

Slit the fixture to let it collapse around the bottle, then chuck up the first victim with support from a conveniently sized drill chuck in the tailstock:

Shower Curtain Anchor – cutting bottle

I did a better job of cutting the second bottle to the proper length:

Shower Curtain Anchor – parting base

Nibble disks from sheet metal, half-fill the bottle bottoms with steel-filled (and, thus, magnetic!) JB Weld epoxy, insert disks, add sufficient epoxy to cover the evidence:

Shower Curtain Anchor – epoxy curing

Fast-forward to the next day, punch out two disks of double-sided foam tape:

Shower Curtain Anchor – adhesive foam

Affix, install, and it’s all good.

Actually, it’s not. The ceramic magnets are so weak they don’t hold the curtain nearly well enough to satisfy me. The next anchor iteration should have embedded neodymium magnets to attract the curtain’s crappy ceramic magnets, but this is Good Enough™ for now.

2019-07-26
Kinesis Freestyle 2: Steel Tactile Bumps

Adding tape bumps to the worn Kinesis keyboard demonstrated I really need tactile home keys, so I popped the tops and fired up the Sherline mill:

Kinesis keyboard – 2 mm drilling

That’s a genuine 2 mm carbide end mill, poked 1 mm into the key cap, snuggled right up against the front edge.

Two epoxy dabs and some wiping later:

Kinesis keyboard – 2 mm tactile bearings

The careful alignment on the F key tells you I did it first; obviously, I should make better fixtures.

The holes could be slightly larger and maybe slightly deeper, but the bearings feel just right.

Indeed, they work so well a ball now distinguishes the far-flung Delete and Backspace keys:

Kinesis keyboard – 2 mm bearing – Delete key

Now, to see how long the epoxy lasts …

2019-07-24
Mini-Lathe Cut-Off Tool Holder: Improved Clamp Screw

Apparently all mini-lathe cut –off tool holders suffer from the same problem:

Lathe Cutoff Tool – OEM swaged screw

The clamp tightening screw is made from butter-soft Chinese steel with a swaged hex socket. As you’d expect, the hex wrench eventually (as in, after a few dozen adjustments, tops) rips the guts right out of the socket.

The screw has a M6×1.0 mm threads, but the thread around the hex recess is left-handed. While I could, in principle, print a 127 tooth change gear, rebuild the lathe’s banjo to accommodate it, then single-point a backassward M6 thread, it’s easier to just use a standard socket head cap screw:

Lathe Cutoff Tool – rebuilt screw

The clamp screw passes through the block at an angle:

Lathe Cutoff Tool – blade view

Fortunately, the screw is perpendicular to the angled side over on the left, making it easy to clamp in the Sherline’s vise:

Lathe Cutoff Tool – aligning to screw

Using the laser aligner seemed like a good idea at the time, but the top of the screw wasn’t particularly well-centered on the hole’s axis. I couldn’t screw the left-hand part (with the socket) in from the bottom and center the block near its surface, because then I couldn’t extract the screw before proceeding.

I used a diamond burr to grind out a flat for the screw head:

Lathe Cutoff Tool – clearing screw recess

The flat came from about twenty manual G2 I-2.5 full-circle passes, stepping down through the hard steel block 0.1 mm per pass, at a too-slow 4000 RPM and a too-fast 30 mm/min feed, with plenty of water squirted from one side into a shop vac snout on the other. The doodle in the background of the first picture shows a first pass at the layout, with the burr centered at X=-2.5; I actually did the grinding from X=+2.5 so most of the passes started in thin air.

The screw head started just shy of 10 mm OD and the burr just over 5.2 mm, so the ensuing 5 mm circles created a flat barely large enough. If the flat were perfectly centered on the screw axis, I wouldn’t have had to grind out another millimeter on the left side (toward the bottom of the tool holder body), but it worked out OK:

Lathe Cutoff Tool – 6 mm SHCS test fit

The trial fitting also showed the head stuck out ever so slightly beyond the far side of the block, where it would interfere with the blade, so I turned off 0.4 mm off its OD.

If I had a 50 mm SHCS in hand, I’d have used it. Instead, I extended the threads of a 75 mm screw, then lopped off the end to the proper length. I’ll spare you the ordeal, including the moment when I reached for the cutoff tool to shorten the screw. A bag of such screws will arrive shortly, in preparation for future need.

Now the [deleted] cut-off holder works the way it should have from the beginning.

2019-07-22
MPCNC: Calculating Spring Rates

Calculate the spring rates for the drag knife, diamond engraver, and collet pen holders by measuring the downforce every 0.5 mm (or so):

LM12UU Collet Pen Holder – spring rate test

Then plotting the data points and eyeballing a straight-line curve fit:

MPCNC – Drag Knife Holder – spring constant

Doing it on hard mode definitely has a certain old-school charm. The graph highlights mis-measured data and similar problems, because, if you don’t see a pretty nearly straight line, something’s gone awry.

But we live in the future, so there’s an easier way:

Droid48 – Spring Rate – Linear Fit coefficients

Well, OK, it’s the future as of the early 1990s, when HP introduced its HP 48 calculators. I’m using the Droid48 emulator on my ancient Google Pixel: living in the past, right here in the future.

Start by firing up the STAT library (cyan arrow, then the 5 key), selecting Fit Data … from the dropdown list, then selecting the Linear Fit model:

Droid48 – Spring Rate – Linear Fit screen

Then tap EDIT and enter the data in a tiny spreadsheet:

Droid48 – Spring Rate – Linear Fit data

My default “engineering mode” numeric display format doesn’t show well on the tiny screen. Tapping the WID→ key helps a bit, but shorter numbers would be better.

With the data entered, set an X value and tap the PRED key to get the corresponding Y value:

Droid48 – Spring Rate – Linear Fit prediction

Tapping the OK button puts the line’s coefficients on the stack, as shown in the first picture. Write ’em on a strip of tape, stick to the top of the holder, and it’s all good:

LM12UU Collet Pen Holder – test plot – overview

Works for me, anyhow.

HP still has the HP 48g manuals online. The (unofficial) HP Museum has a page on the HP 48S. More than you want to know about the 48 series.

2019-07-18
MPCNC: Diamond Drag Engraving Speed Tests

The MPCNC isn’t the most stable of CNC machine tools, given its large masses and 3D printed structure. My early plotting pen tests suggested speeds around 250 mm/min were appropriate:

MPCNC – GCMC Text – 250 mm-min

Diamond drag engraving produces a thinner line and makes the wobbulations more obvious:

MPCNC Engraving Speed Test A – 600-900 mm-min

Another test showed similar results:

MPCNC Engraving Speed Test B – 700-900 mm-min

Slowing down definitely reduces the shakes:

MPCNC Engraving Speed Test B – 100-300 mm-min

Producing the best results takes quite a while:

MPCNC Engraving Speed Test A – 50-200 mm-min

Similar results on another test:

MPCNC Engraving Speed Test C – 50-150 mm-min

Those “mm/s” labels are typos; they should read “mm/min”. Plotting at -1.0 mm on scrap CDs and DVDs produces a downforce around 200 g.

Eyeballometrically, 100 mm/min seems fine, but 50 mm/min (I’d likely use 60 for a nice round 1 mm/s) eliminates all the shakes.

Smooth curves, like Guillloché patterns, can run much faster, because they don’t have abrupt direction changes. This 3-½ inch hard drive platter has text engraved at 100 mm/min and the pattern at 600 mm/min, both at -3.0 mm for 300 g of downforce:

MPCNC Engraving – Guilloche drive platter test

A closer look at the text:

MPCNC Engraving – hard drive platter – detail A

And some digits:

MPCNC Engraving – hard drive platter – detail B

When I want to brand an engraved CD, this will suffice:

MPCNC Engraving – CD attribution text

All in all, the MPCNC engraves much better than I expected!

2019-07-17
Drag Knife Blade Ejector Handle

The LM12UU drag knife holder buries the blade ejector pin deep inside the machinery:

Drag Knife – LM12UU ground shaft – assembled

So a handle with a pin makes sense:

LM12UU Drag Knife Ejector Pin Pusher

It’s a variant Sherline tommy bar handle, so there’s not much to say about it.

The dark butt end comes from the traces of the black filament I used for the previous part. Even after flushing half a meter of orange through the hot end, you’ll still see some contamination, even with the same type of plastic. Doesn’t make much difference here, though.

2019-07-16
Power Lift Chair Upholstery Protection

For reasons not relevant here, we have a power lift chair which has been shedding upholstery tufts since the day we got it. After realizing this wasn’t going to stop on its own, I spent a while poking around underneath and discovered the steel struts supporting the leg rest rub along the upholstery during their entire travel:

Lift chair – strut vs upholstery

Apparently, the padding behind the upholstery pushes it a bit further out than the original design could accommodate, letting the raw edges on the steel struts shave off the fuzz.

I put relatively smooth stainless steel tape on all the protrusions and bent it around the rough edges:

Lift chair – strut smoothing

Those steel folds are smoother than they appear.

It’s not obvious this will solve the problem, but the struts seems to be scraping off much less fuzz than before, so it’s a step in the right direction.

Why is it all of today’s consumer products require 10% more engineering to work in the real world?

2019-07-14